1. Technical Field
The invention includes embodiments that may relate to an electrically conducting composition. The invention includes embodiments that may relate to a method of making the electrically conducting composition.
2. Discussion of Related Art
Electrically conductive compositions may be used for a variety of applications. Conductive compositions capable of becoming electrically resistive because of a change in temperature may be used in, for example, electronic devices, over-current protection devices, or electrical heaters.
At low temperatures, the resistance of the electrically conducting composition may be low and may allow a large amount of electrical current to flow through the composition. As the temperature is increased up to a point, there may be a large increase in the electrical resistivity of the composition. A function/curve of the electrical resistivity with temperature may have a positive slope and within this temperature range the electrically conducting composition may have a positive temperature coefficient of resistance (PTCR). As the temperature is raised further, the electrical resistivity of the composition may decrease with temperature and the electrically conducting composition may display a negative temperature coefficient of resistance (NTCR).
PTCR compositions may include an electrically conductive filler, such as carbon black, dispersed in an olefin-based crystalline polymeric matrix or hard metal fillers dispersed in a semi-crystalline or amorphous polymeric matrix. In some PTCR compositions, the PTCR effect may be related to a melting temperature of the polymeric matrix. In other PTCR compositions, a mismatch between the coefficient of thermal expansion between the polymer and the filler may result in a localized disruption in the electrically conductive network, resulting in the PTCR effect. Factors such as the polymer properties and thermal history may effect the electrical properties of the composition. Because at least the thermal history may change, the properties may not be reproducible. Alternative PTCR materials may include polycrystalline ceramic materials that may be made semi-conductive by addition of dopants. Ceramic-based materials may have to be sintered to form electrical articles and may not be processed into articles having a desired shape, mechanical property, or both the desired shape and mechanical property.
It may be desirable to have conductive compositions with electrical and processing properties that differ from those properties of currently available compositions. It may be desirable to have an electrically conductive composition produced by a method that differs from those methods currently available.